As the input and output voltages in a step-down switching voltage regulator get closer in voltage level, the voltage potential across the energy storage inductor of the regulator decreases, causing the inductors rate of energy storage to decrease. Referring to FIG. 1, there is shown a prior art step-down switching voltage regulator 100. Current flows in regulator 100 from the battery (Vin), through inductor (L) and then to the load components, capacitor (C) and resistor (R), when transistor switch (Q1) is "on" (activated). When transistor switch (Q1) is "off" (deactivated), diode (D) conducts, maintaining a current loop with inductor (L) and load (R) until transistor (Q1) is turned "on". Once transistor (Q1)is turned "on", diode (D) is biased "off" again. The controller used in voltage regulator 100 controls the duty cycle (the rate at which the transistor is turned on and off) of transistor Q1 in order to maintain a constant output voltage to the load (R). The divider circuit formed by resistors R1 and R2 is used to inform the controller the output voltage level, while the divider formed by R3 and R4 is used to inform the controller the voltage level of the input voltage source.
The problems encountered with the prior art voltage regulator shown in FIG. 1 are several, as previously discussed, the amount of energy storage which is achieved by inductor (L)is dependent on both the input and output voltages of the regulator. Also, the commutating diode (D) being a fairly high dissipation device (approximately providing for a 0.5 volt voltage drop), takes away much of the circuits efficiency during the time transistor (Q1) is turned "off", especially as Vout gets lower in voltage level and the voltage drop across diode (D) becomes a larger percentage of the overall voltage drop in the loop. A need thus exists for a switching voltage regulator which is dependent only on the input voltage level and which can provide for lower output voltage levels.
In switching audio amplifier systems as the audio volume setting and the battery supply voltage vary, the efficiency of the amplifier also varies. Variable supply speaker loads exist in the field of audio amplifiers, however they require a transformer to move both terminals of the speaker load about a ground reference as taught in U.S Pat. No. 4,445,095, entitled "Audio Amplifier", by Robert W. Carver. The addition of a transformer adds both expense and increases the size of the audio amplifier circuit. A need exists for an audio amplifier system which provides for substantially constant efficiency over varying voltage and volume settings without the need for the use of a transformer.